Limited availability and hence the volatile costs of petroleum based liquid fuels, such as gasoline, diesel fuel, jet fuel, etc., have increased usage of alternative fuel options, such as liquefied fuel gases. Examples of such liquefied fuel gases include Liquefied Natural Gas (LNG), Liquefied Hydrogen (LH), Refrigerated Liquefied Methane (RLM), etc. Such liquefied fuel gases are typically liquefied at very low (cryogenic) temperatures, such as −130° C. to −170° C.
Generally, liquefied fuel gases are stored in cryogenic fuel tanks, which are maintained at a low temperature as required by the fuel gas to remain in liquid form. Natural Gas (NG) is one of the most popular alternative fuel option that is used by internal combustion engines as Liquefied Natural Gas (LNG) or Compressed Natural Gas (CNG). In general, a liquefied gas is converted into gaseous form before being supplied to the engine for combustion.
Cryogenic fuel systems for delivering gaseous fuel to the engine typically include a high pressure cryogenic fuel pump used to supply fuel from the cryogenic fuel tank to a vaporizer. The vaporizer converts the fuel from liquefied form into gaseous form, which is subsequently supplied to the engine for combustion. Typically, high pressure cryogenic fuel pumps have their respective rated maximum and minimum speed, at which these pumps may operate. Operational speed of the high pressure cryogenic fuel pump may be adjusted based on a fuel demand of the engine and according to the mechanical limitations of the high pressure cryogenic fuel pump. However, many times, such as for low load and idle operating conditions, engine fuel demand is much less than what the cryogenic fuel pumps can deliver at their minimum rated speed (also referred to as the minimum discharge output of the pump). Therefore, the cryogenic fuel pumps may not be sufficiently capable of fueling the engine, say, below their minimum rated speed and capability, in order to meet the low engine fuel demands at low load and idle operating conditions. Thus, in one of such scenarios, the cryogenic fuel pumps are completely switched off to stop pumping any fuel to the engine, which may stop the engine as well. In another such scenario, the cryogenic fuel pumps could be run on the minimum rated speed to discharge their minimum output of fuel, which exceeds the flow to be supplied to the engine. The excess fuel can be separated out and returned to the storage tank. This results in wastage and excessive warming of fuel which is beyond what is required by the engine. In both the scenarios, running the engine in low load and/or idling conditions becomes a challenge.
U.S. Pat. No. 6,663,350 ('350) describes a high pressure pump suitable for Liquefied Natural Gas and other cryogenic liquid fuel powered vehicles. The high pressure pump is a reciprocating pump which includes a liquid pumping portion and a vapor compressing portion, operating in concert so that it is possible to locate the pump above a source of saturated LNG and to supply high pressure LNG to the engine. However, the '350 patent does not take into account the low engine fuel demands and/or idle conditions of the engine. Thus, there is a need for a better way to operate the cryogenic fuel systems in order to handle low and/or idle operating conditions of the engine.